Bonding pad on a back side illuminated image sensor

Abstract

A bonding pad structure comprises an interconnect layer, an isolation layer over the interconnect layer, a conductive pad, and one or more non-conducting stress-releasing structures. The conductive pad comprises a planar portion over the isolation layer, and one or more bridging portions extending through at least the isolation layer and to the interconnect layer for establishing electric contact therewith, wherein there is a trench in the one or more bridging portions. The one or more non-conducting stress-releasing structures are disposed between the isolation layer and the conductive pad. The trench is surrounded by one of the one or more non-conducting stress-releasing structures from a top view.

What is claimed is: 
     
       1. A bonding pad structure, comprising:
 an interconnect layer; 
 an isolation layer over the interconnect layer, wherein a trench is provided in the isolation layer; 
 a conductive pad comprising:
 bridging portions over the interconnect layer, wherein each bridging portion includes a side portion extending along a sidewall of the trench in the isolation layer and a bottom portion contacting a top surface of the interconnect layer and forming a hollow gap with the side portion within each of the bridging portions in the trench; and 
 a planar portion connecting adjacent bridge portions; and 
 
 one or more non-conducting stress-releasing structures disposed between the isolation layer and the conductive pad, wherein the one or more non-conducting stress-releasing structures contact surfaces of the bridging portions and the planar portion of the conductive pad. 
 
     
     
       2. The bonding pad structure of  claim 1 , wherein a first sidewall of the one or more non-conducting stress-releasing structures contacts a sidewall of the bridging portions of the conductive pad, and a second sidewall of the one or more non-conducting stress-releasing structures contacts a sidewall of the planar portion of the conductive pad. 
     
     
       3. The bonding pad structure of  claim 1 , wherein a bottom surface of the one or more non-conducting stress-releasing structures contacts a top surface of the isolation layer. 
     
     
       4. The image sensor device bonding pad structure of  claim 1 , wherein each of the one or more non-conducting stress-releasing structures has a configuration of a generally rectangular wall. 
     
     
       5. The bonding pad structure of  claim 1 , further comprising a conductive ball bonded with the planar portion of the conductive pad. 
     
     
       6. The bonding pad structure of  claim 1 , wherein a first part of the conductive pad covers a top surface of the isolation layer and a second part of the conductive pad covers a top surface of the one or more non-conducting stress-releasing structures, wherein the first part of the conductive pad is lower than the second part of the conductive pad, thereby forming a step. 
     
     
       7. The bonding pad structure of  claim 1 , wherein each of the one or more non-conducting stress-releasing structures is fully enclosed only by the isolation layer and the conductive pad. 
     
     
       8. The bonding pad structure of  claim 1 , wherein each of the one or more non-conducting stress-releasing structures is in direct contact with both the isolation layer and the conductive pad. 
     
     
       9. The bonding pad structure of  claim 1 , further comprising an interlayer dielectric layer between the interconnect layer and the isolation layer, wherein the bridging portions extend through the interlayer dielectric layer. 
     
     
       10. A bonding pad structure, comprising:
 an interconnect layer; 
 an interlayer dielectric layer formed over the interconnect layer; 
 an isolation layer formed over the interlayer dielectric layer, wherein a trench is provided through the interlayer dielectric layer and the isolation layer; 
 a non-conducting stress-releasing structure disposed over the isolation layer, wherein the non-conducting stress-releasing structure has a configuration of a surrounding wall with an opening extending through an inner surface of the surrounding wall; and 
 a conductive pad comprising:
 bridging portions within the trench, wherein each bridging portion includes a side portion and a bottom portion, the side portion extends along a sidewall of the trench in the interlayer dielectric layer and the isolation layer, and is connected by the bottom portion on a top surface of the interconnect layer for establishing electrical contact therewith, the each bridging portion only partially filling the opening and resulting in a hollow gap in the opening; and 
 a planar portion overlying the isolation layer and connecting adjacent bridging portions. 
 
 
     
     
       11. The bonding pad structure of  claim 10 , wherein the non-conducting stress-releasing structure comprises an oxide material. 
     
     
       12. The bonding pad structure of  claim 10 , wherein the non-conducting stress-releasing structure comprises the same material as the isolation layer. 
     
     
       13. The bonding pad structure of  claim 10 , wherein the surrounding wall is generally rectangular from a top view. 
     
     
       14. The bonding pad structure of  claim 10 , further comprising a conductive ball bonded with the planar portion of the conductive pad. 
     
     
       15. A bonding pad structure, comprising:
 an interconnect layer having a conductive feature; 
 an isolation layer over the interconnect layer and providing a trench; and 
 a non-conducting structure enclosed by the isolation layer and a conductive pad; 
 wherein the conductive pad comprises:
 a first portion overlying the isolation layer and contacting a first sidewall of the non-conducting structure, and 
 a second portion extending from the first portion, through the trench, and to the interconnect layer and contacting the conductive feature, wherein the second portion covers a top surface of the non-conducting structure and only partially fills the trench and leaves a hollow gap in the trench. 
 
 
     
     
       16. The bonding pad structure of  claim 15 , wherein the non-conducting structure is part of a generally rectangular wall structure from top view. 
     
     
       17. The bonding pad structure of  claim 16 , wherein the generally rectangular wall structure provides sidewalls for a trench through the isolation layer and over the interconnect layer. 
     
     
       18. The bonding pad structure of  claim 17 , further comprising an interlayer dielectric layer between the interconnect layer and the isolation layer, wherein the trench also goes through the interlayer dielectric layer. 
     
     
       19. The bonding pad structure of  claim 15 , wherein a top surface of the second portion covering the top surface of the non-conducting structure is above a top surface of the first portion contacting the sidewall of the non-conducting structure. 
     
     
       20. The bonding pad structure of  claim 19 , wherein the second portion extends along a second sidewall of the non-conducting structure.